Conjugated diene rubbers (for example, styrene-butadiene copolymers) obtained by emulsion polymerization methods are known as rubbers for automotive tires. A variety of conjugated diene rubbers that can realize an excellent fuel efficiency performance have been introduced in recent years with the expectations for improved automotive fuel efficiency performance.
As an example, a conjugated diolefin (co)polymer rubber with the following characteristics (1) to (3) and a rubber composition containing the conjugated diolefin (co)polymer rubber have been proposed: (1) it is a (co)polymer rubber of a conjugated diolefin or a conjugated diolefin and an aromatic vinyl compound; (2) it has a primary amino group and an alkoxysilyl group bound to the (co)polymer chain; and (3) a monomer having two or more functionalities is copolymerized in the (co)polymer chain, and/or, at least a portion of the (co)polymer chain is coupled with a coupling agent having two or more functionalities. (Patent Document 1).
As another example, a modified diene polymer rubber and a rubber composition containing the modified diene polymer rubber have been proposed wherein the modified diene polymer rubber is obtained from a step 1 of obtaining an active polymer having an alkali metal terminal by polymerizing a conjugated diene monomer or polymerizing a conjugated diene monomer and an aromatic vinyl monomer in a hydrocarbon solvent in the presence of an alkali metal catalyst and a step 2 of obtaining a modified polymer rubber by reacting the active polymer with a compound represented by a specific formula (Patent Document 2).
Moreover, as a method for producing a modified polymer that has an increased interaction with a silica and carbon black and that can provide improved failure characteristics, abrasion resistance, and low heat build-up performance, a method of performing a primary modification reaction, in which a hydrocarbyloxysilane compound is reacted with the active site of a polymer that has an organometal active site in the molecule, and subsequently performing a secondary modification reaction, in which a hydrocarbyloxysilane compound is reacted via a condensation reaction between hydrocarbyloxysilyl groups each other (Patent Document 3).